| As the foundation and development of integrated electro-optics (EO) and technique of density wavelength divided multiplex (DWDM), the information in communications field has been greatly increased day by day. People need large information transforming capacity and need the much fast signal transforming speed (up toμs) according with the capacity. Some traditional communication technologies and devices could not fulfill the demands of applications. All optical communication networks will benefit to realize"information superhighway"and digital communication with high speed and large capacity in the world. Achieving the goal of optical network includes two parts: one part is that the optical network gains a wider ground in the aspect of transmission network, and covers the connection network, which is"fiber to the home"we called; the other is that the EO-OE (optical-electronics) conversion is reduced in the process of information conversion, makes a good use of the high light speed and finishes the optical conversion and access directly.As key devices,optical switches are used chiefly in the optical cross connection system in the optical network. Optical switches can fulfill many functions such as routing, selection to optical wavelength and OXC etc, integrated optic switch arrays are also key devices in realizing wavelength multiplex and optic cross connections. Electro-optic switches are based on electro-optic, or well-known Pockels effect. Such kind of switches is known as their advantages of fast speed, low insertion loss, high extinction ration and long life.The structure of M-Z polymer electro-optic switch consists of waveguide and electrodes. The performance of an electro-optic switch is decided by its electrode system when the part of waveguide has been fabricated. In this dissertation, studies of microwave electrode of polymer electro-optic switch, including theoretic analysis, optimizing, design, fabrication and testing, have been carried out. Microwave electrode is known as the traveling-wave electrode, there are three regions in the electrode system. Every region has different structures which influence several features of an electro-optic switch. But the design of interaction region is the most important part. Once the structure of this region is decided, other regions can be calculated by the software to produce a complete switch.This study mainly covers the following aspects:1. Theory and AnalysisThe history and the latest developments in electro-optic switches have been introduced. The working principle of the electro-optic effects and electro-optic Mach-Zehnder interferometer switches are analyzed. By analyzing many kinds of configurations of the micro-wave electrode system of polymer electro-optic switches, taking into account the laboratory conditions and performance requirements of the micro-wave electrode system of polymer electro-optic switches,we selected coplanar waveguide (CPW) traveling-wave electrode and microstrip line (MSL) traveling-wave electrode.2. DesignWe need to calculate the features, such as Vπ,Neff,3dB f,Z0 according to the width,thickness and electrodes gap to design the electrode system, and all the calculations are the fundamental of electrode design. In this dissertation, we designed the CPW and MSL electrode system.Specific design method is as follows:(1) The establishment of theoretical calculation model. All of this work provided a theoretical basis for designing the microwave electrode. We got the analytical expression of the characteristic impedance Z0, microwave equivalent refractive index Neff, ohm lossαc, dielectric lossαd, and other parameters about CPW traveling-wave electrode system according to partial capacitance method. According to full-wave analysis, we got approximate formula of Z0, Neff,αc andαd about MSL traveling-wave electrode.(2) Software simulation and theoretical verification, it ensured the reliability of the design value. The main performance parameters of electrode system are given. By combining software simulation and theoretical calculations (the errors in the calculation are acceptable), we discussed the relationship between size of electrode system and performance parameters such as Z0, Neff,α0, Vπ, 3dB f, we calculated structural parameters of the electrode and its performance indicators, and determined the size of the value of the CPW and MSL electrode such as electrode width W, electrode spacing G, the electrode thickness T, the interaction length L. The CPW traveling-wave electrode of polymer electro-optic switches is designed finally with Vπ=9.523V, 3dB f=20.014GHz (Si substrate); Vπ=5.952V, 3dB f=273.11GHz (Quartz substrate); Vπ=4.96V, 3dB f=52.93GHz (Glass substrate). The MSL traveling-wave electrode is also designed finally with Vπ=12.678V, 3dB f=57.875GHz.We summarized the results of design and got the following conclusions:3dB bandwidth is limited by N0 -Neff. Microwave equivalent refractive index of MSL will not be affected by the substrate material, it is mainly determined by the polymer dielectric constant. But microwave equivalent refractive index of CPW is mainly determined by substrate material. Increasing the electrode thickness can effectively reduce the transmission loss.(3) Fabricating processThe devices have been produced through the semiconductor process. After many experiments, we overcome the difficulties such as side corrosion, poor photoresist adhesion. Several CPW traveling-wave electrodes and MSL traveling-wave electrodes with different substrate materials and dielectric layers were fabricated. A microwave probe used for high-frequency test is designed and fabricated.(4) Microwave testingIn this thesis, microwave network theory and testing methods of the two-port scattering parameters were studied, a testing system for electrodes was built by using microwave vector network analyzer. The S parameters are obtained by test. By comparing the test results, we got the following conclusion: the loss of CPW traveling-wave electrode based on silicon substrate is larger than that on other substrates, and the loss of CPW traveling-wave electrode based on quartz substrate is smaller than that on other substrates, this is consistent with the theoretical analysis. In 0~4GHz frequency range, microwave electrodes have a good response curve of S21. |
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